Generally, a bandgap reference voltage generator (hereinafter abbreviated BGR) is used for an analog circuit including a high resolution comparator, an analog to digital (A/D) converter, a digital to analog (D/A) converter and/or a data converter and also is used for c circuit for supplying a reference voltage (Vref) of a memory circuit. The BGR needs to supply a stable reference voltage (Vref) despite a change of an external design environment, e.g., a change of power, temperature, process parameter or the like.
Generally, in order to secure a stable operation characteristic against a change of an external design environment for a system circuit, a BGR for supplying a reference voltage or current constant in such an external environment change as a supply voltage is used as a bias power supply device. A related reference voltage generating circuit includes a self-bias current mirror circuit to provide a BGR with a uniform bias voltage (VBIAS). Yet, this self-bias current mirror circuit may cause an undesired problem of putting a bias voltage (VBIAS) in a zero state for example.
Therefore, a start-up circuit preventing a bias voltage from being put into a zero state in a normal operation of a self-bias current mirror circuit may be additionally included in a reference voltage generating circuit. The start-up circuit helps an initial operation of the self-bias current mirror circuit only. But, the start-up circuit should not affect an operation of the self-bias current mirror circuit in a manner of being separated from the self-bias current mirror circuit if the self-bias current mirror circuit enters a normal operation state.
However, related start-up circuits may enter a power-up state, in which a supply voltage (VDDA) of an analog type ascends, if an external design environment changes. In the power-up state, this may cause a problem that the start-up circuit may affect the self-bias current mirror circuit to raise a reference voltage generated from the BGR. Moreover, in this case, since a current flowing in the self-bias current mirror circuit increases, a current consumed by the self-bias current mirror circuit may be raised irrespective of an operation of the self-bias current mirror circuit.